Electrolytic cells have been developed which utilize ion-exchange membranes for the selective migration of ions therethrough under the influence of a DC potential. Typical of these are the cells disclosed in U.S. Pat. No. 3,124,520 and 3,262,868 to Juda et al. These Patents describe cell systems in which porous electrodes are wetproofed by attaching solid ion exchange membranes to their surfaces. However, to separate anolyte and catholyte a cation exchange membrane is fixed between the electrodes and said electrodes are spaced apart from the membrane. Both Patents describe cells which utilize paired combustible and oxidant electrodes, including oxygen electrodes for the production of caustic and chlorine. Oxygen or air is utilized as a depolarizer in membrane cells employing porous cathodes.
U.S. Pat. No. 3,963,592 to Lindstrom describes a chloralkali electrolytic cell which is directed primarily to supplying gaseous hydrogen to the anode where it is oxidized to hydrogen ions. These ions are then caused to react with chloride ions at the anode to form hydrochloric acid as the product instead of chlorine. This Patent also describes the specific nature of the porous anode. The cells employed may include airdepolarized cathodes; however, no structures are disclosed different from those in the other cited art on air-depolarized cathodes for chlor-alkali cells.
U.S. Pat. No. 3,117,034 to Tirrell discloses a fuel gas electrode which utilizes a cation-permeable membrane and an anode which is intimately and physically in contact with said membrane. There is no teaching of a chlor-alkali cell in which an electrolyte is electrochemically converted into a new species which, in turn, must be kept apart from the bulk electrolyte. Indeed, the catholyte in this Patent is the acid solution which separates the membrane from the cathode.
U.S. Pat. No. 4,039,409 to LaConti also discloses a catalytic anode for use in an electrolytic cell for gas concentration and generation comprising a reduced alloy of platinum and ruthenium. The cell of this Patent comprises a pair of electrodes on either side of an ion-permeable membrane. Oxygen gas is generated at the catalytic anode.
U.S. Pat. No. 3,926,769 to Gritzner discloses an electrolytic cell which utilizes a diaphragm for the production of alkali metal hydroxides and gaseous chlorine. This Patent describes, with reference to the embodiment of FIG. 1, the air depolarization of a cell cathode in which the diaphragm is spaced apart from the catalyzed cathode by an appreciable distance over the catholyte zone resulting in a considerable power loss.
U.S. Pat. No. 3,923,628 to Gritzner covers an electrolytic brine cell in which the anode and cathode are spaced apart from one another and separated by a diaphragm. An oxidizing gas is brought into contact with the cathode for the purpose of depolarizing it and bringing under control the formation of hydrogen gas. However, it appears from the mixed results in Tables I-III and the specific embodiments that the depolarization procedure does not uniformly improve cell efficiency or minimize hydrogen gas formation. Indeed, Examples 1-33 of this Patent do not even mention hydrogen gas control.
In this Gritzner reference (U.S. Pat. No. 3,923,628), the air or oxygen used for depolarization purposes is pumped into a compartment partially defined by the cathode and it is then summarily withdrawn. The operating pressures for this procedure are not disclosed. Accordingly, there is no disclosure of means for achieving measurable contact between the oxygen-containing gas and the cathode.